Electro-optical removal of plastic layer bonded to a metal tube

ABSTRACT

A method for preparing a multi-layer tube, useful prior to endforming for brakeline connections, comprises the steps of forming a metal tube having an outer surface and an end and bonding a corrosion resistant layer to the metal tube outer surface. A surface treatment layer is bonded to the corrosion resistant layer. A first polymeric layer is extruded onto the metal tube, such that it bonds to the surface treatment layer; and a second polymeric layer is extruded onto the metal tube, such that it bonds to the first polymeric layer. The method further comprises the step of vaporizing and removing at least a portion of the first and second polymeric layers from an area adjacent the end by rotating an axially defocused, generally elliptical cross-sectionally shaped laser beam 360° about the area, while leaving the corrosion resistant layer intact.

BACKGROUND OF THE INVENTION

This invention relates to electro-optical removal of a plastic layerbonded to a metal tube, and more particularly to laser removal of theplastic layer without damage to any corrosion resistant layer bonded tothe metal tube.

In the automotive industry, it is typical to create what are called"ISO" or "SAE" flared endforms on high pressure fluid conduits,particularly brake tubes. Automotive manufacturers mandate that thefront and back flare faces be free from substantial polymeric layers.The manufacturers are concerned over a potential loss of assembly torqueover the long term of a vehicle's life which could occur if therelatively soft polymeric material, eg. nylon, should extrude out of thesealing area and fitting compression area after assembly.

The polymeric material is present on the outer surfaces of the fluidconduits in order to greatly enhance the corrosion resistance of themetal tubing comprising the conduits. Thus, manufacturers of theseconduits, especially when end use will be under a vehicle body, do notwant to remove any more of this corrosion resistance-enhancing polymericmaterial than is necessary, eg. for example, not past a flare into thestraight section of the tube. Further, the metal tubing generally has acorrosion resistant layer bonded to the metal tube outer surface. Assuch, it is highly desirable that any removal process not damage thecorrosion resistant layer beneath the polymer, nor the outer surface ofa bare metal tube (if no corrosion resistant layer has been bondedthereto).

Several methods have been tried, with varying levels of success.However, each method has serious drawbacks, preventing the use thereof.A rotary lathe cut method uses a chuck holder with lathe style squaretool bits. It is mounted on a standard rotary head deburring unit. Themethod is simple and reliable; however, results revealed that the nylondoes not easily machine off. Strings/burrs are left on, particularly atthe transition line. Further, infinite adjustments and measurementswould have to be made due to the tube O.D. variance, to attempt toprevent cutting through the substrate.

A method using rotary brushes employs the use of a grinding wheel headdriving a brush. The tube was held and rotated by hand. The area wherethe coating is to be removed is forced into the brush, and thetransition line is determined by locating a protective sleeve over thetube at the desired location. The sleeve used is about 2" long and heldin place with a set screw. Unfortunately, this method requires a complexadjustment mechanism to compensate for brush wear. Further, it is verydifficult to determine if only the nylon would be removed. Other brusheshave been tried with no real success.

A square head punch method uses a blunt nose punch that has a fixeddiameter hole that goes over the steel tube and pushes the nylon to adesired distance. The "pushed back" nylon material is then cut off andremoved via a rotary lathe cut system. This method has the drawback thatit would be impossible to predict the amount (thickness) of nylonremoved or conversely, left on, and it would dig into any corrosionresistant coating.

A water jet knife method involves the use of a high pressure water jetsystem to cut and blow off a nylon coating without affecting a ZnAlsubstrate. The method involves rotating the tube at high rpm while astationary high pressure water jet removes the coating. The travel speedof the jet was 12"/minute (=0.2"/sec.). The entire system uses 50 Hp ofpower (=37.3 KW). This method does appear to remove the nylon coatingwithout affecting the corrosion resistant coating, it is forgiving tothe O.D. and ovality variances and has a very fast cycle time. However,it is difficult and costly to have high rpm tube rotation; the systemuses ultra clean water as the removal medium (which is expensive), andit is not economical to recycle the water. The water will be a problemto the exposed ends of the tube. A further drawback is that there arehigh maintenance costs for the system.

In German Patent No. DE 44 13 218, there is disclosed a device for thecontactless removal of a layer of lacquer or plastic, for example PTFE,from a component by means of a pulsed laser beam. This method removes acoating without damage to a primer underneath. However, it appears thatthe laser energy is guided to any location within a semicircular workspace. As such, it appears that the laser energy would not be rotatablearound a workpiece, thus requiring rotation of the workpiece, which addsto production costs. Further, it does not appear that the disclosedmethod removes more than a single layer. A further drawback is that thedisclosed machine, comprising articulated opto-mechanical arms, islarge, complex and very expensive.

Thus, it is an object of the present invention to provide a method forthe fast, efficient, precise and cost effective removal of one ormultiple polymeric layers from a metal substrate. Further, it is anobject of the present invention to provide such a method which will notdamage the substrate or any corrosion resistant coating thereon. Stillfurther, it is an object of the present invention to provide such amethod which leaves a smooth transition portion to aid in subsequentconnections. It is yet another object of the present invention toprovide such a method which optionally leaves a residue for enhancedcorrosion resistance on the removed surface. It is still another objectof the present invention to provide such a method which is forgiving toouter diameter and ovality variances.

SUMMARY OF THE INVENTION

The present invention addresses and solves the above-mentioned problemsand achieves the above-mentioned objects and advantages by providing amethod for preparing a multi-layer tube, comprising the steps of forminga metal tube having an outer surface and an end and bonding a corrosionresistant layer to the metal tube outer surface. A surface treatmentlayer is bonded to the corrosion resistant layer. A first polymericlayer is extruded onto the metal tube, such that it bonds to the surfacetreatment layer; and a second polymeric layer is extruded onto the metaltube, such that it bonds to the first polymeric layer. The methodfurther comprises the step of vaporizing and removing at least a portionof the first and second polymeric layers from an area adjacent the endby rotating an axially defocused, generally elliptical cross-sectionallyshaped laser beam 360° about the area, while leaving the corrosionresistant layer intact.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects, features, advantages and applications of the presentinvention will become apparent by reference to the following detaileddescription and to the drawings, in which:

FIG. 1 is a semi-schematic perspective view of the electro-opticalremoval apparatus of the present invention;

FIG. 2 is a semi-schematic top view of the electro-optical removalapparatus;

FIG. 3 is a partially cut away, cross sectional view of the removablebushing and adjustable stop, showing a portion of a metal tube insertedwithin the bushing and abutting the stop;

FIG. 4 is a partially cut away, semi-schematic view of the beam deliverysystem;

FIG. 5A is a cross sectional view taken on line 5--5 of FIG. 4 showingthe generally elliptical cross sectional shape of the laser beam as itimpinges the polymeric layer portion of the multi-layer tube;

FIG. 5B is a cross sectional view taken on line 5--5 of FIG. 4 showingan alternate generally elliptical cross sectional shape of the laserbeam as it impinges the polymeric layer portion of the multi-layer tube;

FIG. 6 is an enlarged, cross sectional view of the multi-layer tubetaken on line 6--6 of FIG. 3, with the layer thicknesses exaggerated forpurposes of illustration;

FIG. 7A is an enlarged, partially cut away view of the multi-layer tubeshowing the polymeric layer portion removed, and the tapered transitionportion;

FIG. 7B is a view similar to FIG. 7A, but also showing the ultra thin,corrosion resistance-enhancing polymeric residue;

FIG. 8 is an enlarged, cut away cross sectional view of an SAE-typedouble or inverted flare, showing the lower half of the endform inphantom and showing the laser removed surface on the flare;

FIG. 9 is an enlarged, cut away cross sectional view of an ISO-typeannularly protruding flare, showing the lower half of the endform inphantom and showing the laser removed surface on the flare;

FIG. 10 is a simplified flow diagram of a process according to thepresent invention for extruding multiple plastic layer coatings bondedto a metal tube;

FIG. 11 is a second flow diagram of the process according to the presentinvention; and

FIG. 12 is a detailed flow diagram of a process according to the presentinvention.

DETAILED DESCRIPTION OF THE PREFERRED AND ALTERNATE EMBODIMENTS

Referring now to FIG. 1, the electro-optical system of the presentinvention for removing a plastic layer from the outer surface of a metaltube is designated generally as 10. System 10 is relatively compact andportable, being about 24" wide, 66" high and 60" long (although it is tobe understood that system 10 may be made to varying sizes). System 10includes a programmer 12 for controlling at what position and what axiallength of plastic layer is removed, an RF supply 14 to power the lasergenerator 20, a chilled water supply 16 for cooling the laser generator20, and an air cleaner 18 for removing gasses, fumes, any liquid orparticulate plastic, and/or any other particulate matter which may bepresent. Further details and use of this apparatus 10 will be explainedhereinafter in reference to the method of the present invention.

Referring now to FIGS. 4-6, the method for preparing a multi-layer tube22 according to the present invention comprises the step ofsubstantially removing at least a portion 36 of a polymeric layer,designated generally as 24, from an outer surface circumference 26 of asubstantially non-rotating metal tube 28 having a corrosion resistantcoating layer 30 applied thereto, by axially defocusing a laser beam 32from a pinpoint cross-sectional shape 42 to a generally ellipticalcross-sectional shape 34 onto the polymeric layer portion 36. Thegenerally elliptical cross-sectionally shaped laser beam 34 vaporizesthe polymeric layer portion 36 while leaving the corrosion resistantlayer 30 (or simply the metal tubing substrate, if no corrosionresistant layer 30 is applied) intact. Without being bound to anytheory, it is believed that this phenomenon may occur because thedefocused laser beam, having the unique generally ellipticalcross-section 34 as described herein, causes the laser energy to beabsorbed by the plastic layer or layers in varying degrees, but isreflected by the metal tube 28. Thus, the laser beam 32 removes thepolymeric portion 36, while leaving a smoothly tapered transitionportion 74 (discussed in detail hereinbelow), without damaging thesubstrate.

The axial defocusing is accomplished by a beam delivery system 38. Thesystem 38 comprises a laser beam generator 40 emitting the pinpointcross-sectionally shaped laser beam 42.

It is to be understood that any suitable laser apparatus having asuitable laser beam generator 40 may be used. However, in the preferredembodiment, a CO₂ laser having a wavelength of 10.59 microns is used.This laser may have a power ranging between about 50 Watts and about 240Watts. In the preferred embodiment, either a 100 Watt or a 200 Wattcontinuous laser may be used, as well as any power ranging therebetween.Such lasers are available from synrad in Mukilteo, Washington: the 100Watt laser is commercially available as Model 57-1, and has a sealed,RF-excited, water-cooled laser head; the 200 Watt laser is available asModel 57-2, and has two standard 57-1, 100 Watt laser tubes mounted sideby side, but rotated 90° with respect to each other, feeding an opticalbeam combiner.

The beam delivery system 38 further comprises means, operativelyconnected to the beam generator 40, for defocusing the pinpointcross-sectionally shaped laser beam 42 into the generally ellipticalcross-sectionally shaped laser beam 34. The beam delivery system 38 mayfurther comprise means, operatively connected to the beam generator 40and the defocusing means, for reflecting one of the pinpointcross-sectionally shaped laser beam 42 and the generally ellipticalcross-sectionally shaped laser beam 34 to a position adjacent thepolymeric layer portion 36.

As shown in FIG. 4, the laser beam 42 enters the reflecting means alongan axis 44. The reflecting means comprises a generally C-shaped housing46 which rotates 360° about the axis 44 (see rotational arrow 48). Thehousing 46 has a laser beam entry 50 and a laser beam exit 52. Thereflecting means further comprises a mirror system, designated generallyas 54, disposed within the housing 46, the mirror system 54 adapted toreflect at least one of the pinpoint cross-sectionally shaped laser beam42 and the generally elliptical cross-sectionally shaped laser beam 34from the entry 50 to the exit 52. It is to be understood that the mirrorsystem 54 may be comprised of one or multiple mirrors 54', with themirrors 54' having any suitable size and/or shape. Although theabove-described reflecting means is the preferred embodiment thereof, itis to be understood that the reflecting means may comprise any meanssuitable to achieve the objects and advantages of the present invention.

An example of a suitable reflecting means apparatus having a rotatingmirror system 54 as described above is commercially available from RTMCin Phoenix, Ariz., under the tradename WD-1LTC-100 (one of the WD-1PersonaLaser™ Briefcase Portable series), which is a 100 Watt Turnkeylaser wire stripping system. The WD-1LTC-100 apparatus (which does notinclude the unique defocusing means as described herein) is used tostrip wire, cables, conductors, coaxial cables and the like (primarilyin the aircraft industry) by making a thin cross cut down to the wire orcable surface about the wire or cable circumference, leaving the slugon. The apparatus may also make an axial cut to make the slug easier toremove. In short, the apparatus without the unique defocusing means ofthe present invention basically utilizes the laser beam as a knife.

It is to be further understood that the defocusing means may compriseany suitable means. However, in the preferred embodiment, the defocusingmeans comprises a defocusing lens 56 disposed within housing 46. It isto be understood that any defocusing lens suitable to achieve theobjects and advantages of the present invention may be used. It ispreferred that such a lens have a focal length ranging between about1.5" and about 3", and more preferably between about 2" and about 2.5".An example of such a suitable lens, used in the preferred embodiment, isa ZnSe 2.5" focal length×0.750" cylindrical diameter lens, commerciallyavailable from Level 4 Laser Systems in Novi, Mich. as Model II-VI. Asbest shown in FIG. 4, mirror system 54 reflects pinpointcross-sectionally shaped laser beam 42, defocusing lens 56 is mountedadjacent laser beam exit 52, and generally elliptical cross-sectionallyshaped laser beam 34 is emitted through laser beam exit 52. It is to beunderstood that laser beam generator 40 may be directly adjacent theC-shaped housing 46, as shown in FIG. 4; or it may be offset, as shownin FIG. 2, and transmitted to C-shaped housing 46 via a secondappropriate mirror system 58. In the preferred embodiment, laser 20 isoffset as shown in FIG. 2.

The reflecting means and defocusing means are assembled, as shown inFIGS. 1 and 4, in an environmentally safe manner. System 10 may furthercomprise an air nozzle (not shown) directed at end 60 area, for aidingin blowing off polymeric layer portion 36 from tube outer surface 26.This nozzle may operate within any suitable parameters, however, in thepreferred embodiment, the nozzle operates at 4-8 cfh at 5-10 psi.Interior 94 of C-shaped housing 46 is pressurized, while outside housing46, beam delivery system housing 95 has a vacuum applied theretosufficient to draw out any gasses, fumes, any liquid or particulateplastic, and/or any other particulate matter which may be presentthrough outlet 96 (as shown by arrow 97) to air cleaner 18 (which maycomprise a three stage filtering system), which is then vented toatmosphere. As an example of suitable pressurization, a blower develops160 scfm at 1" water column. Thus, any workers in or near the area ofthe system 10 of the present invention should be safe from any possibletoxicity which may exist during the polymeric layer removal.

Polymer portion 36 is removed in the following manner, as best seen inFIG. 4. An end 60 of multi-layer tube 22 is positioned adjacent laserbeam exit 52 against adjustable stop 62, and multi-layer tube 22 iscentered on axis 44. Tube 22 is received within, and held in place by areplaceable steel entry bushing 64. Bushing 64 may be replaced dependentupon the size of tube 22 to be inserted therein. For example, a 3/16"tube uses an entry bushing 64 having a diameter of approximately0.213"±0.002" (the following bushing diameters are approximately±0.002"): for a 1/4" tube, the bushing diameter would be approximately0.275"; for a 5/16" tube, approximately 0.337"; and for a 3/8" tube,approximately 0.400". As seen in FIG. 3, polymer portion 36 subject toremoval is held between the stop 62 and the bushing 64. This portion 36(shown by brackets in FIG. 3) is the portion that is exposed to thegenerally elliptical cross-sectionally shaped laser beam 34.

Examples of suitable beam cross sections are shown in FIGS. 5A and 5B.As best seen in FIG. 5A, this laser beam 34 has two sides, 66, 68,wherein, preferably, one side 66 is more curved than the other side 68.Even more preferably, as shown in FIG. 5B, the other side 68' isgenerally pointed, and the one side 66' is generally curved. As can beseen in FIGS. 7A and 7B, polymeric layer portion 36 has a first area 70adjacent the tube end 60 and a second area 72 distal from the tube end60. The curved side 66 of the generally elliptical cross-sectionallyshaped laser beam 34 substantially contacts the first area 70, while thegenerally pointed side 68 substantially contacts second area 72.

Without being bound to any theory, it is believed that this uniquegenerally elliptical cross-sectional shape 34 having sides 66, 68 and/or66', 68' aids in forming the generally tapered, smooth transitionportion 74 of the polymeric layer 24, which transition portion 74extends from an upper surface 76 toward the metal tube outer surfacecircumference 26. It is believed that this is due to first area 70seeing a more intense amount of laser energy, while simultaneously, thepolymeric portion 36 sees a progressively less intense laser energy, thecloser the portion 36 is to second area 72.

Referring again to FIGS. 7A and 7B, there is shown a metal tube 28having a first polymeric layer 27 bonded thereto, and a second polymericlayer 29 bonded to first layer 27. The layers 27, 29 are shown asremaining distinct within the transition area 74; however, these layers27, 29 may not be so distinct in practice of the present invention.Nonetheless, the layers 27, 29 (or any number of layers and/orsublayers) within the transition portion 74 will have a sealed, smoothouter surface, leaving no jagged, rough edges exposed to the surface(which may occur in laser removal systems lacking the unique transitionportion 74 of the present invention).

It is to be understood that the length 78 of the smoothly taperedtransition portion 74 may vary substantially. However, in the preferredembodiment, this length 78 is less than about 2 mm (0.08"); and morepreferably is approximately 1.27 mm (0.05"). The polymeric layer portion36 removed also has a length 80 which may vary substantially; however,in the preferred embodiment, this length 80 ranges between about 1 mm(0.04") and about 76.2 mm (3"); preferably length 80 ranges betweenabout 4 mm (0.157") and about 8 mm (0.315"); and more preferably, length80 ranges between about 6 mm (0.236") and about 7 mm (0.276").

Referring now to FIG. 7B, the multi-layer tube 22 may optionally furthercomprise an ultra thin, shiny, corrosion resistance-enhancing polymericresidue 82 on a discrete area of the metal tube outer surfacecircumference 26 after polymeric layer portion 36 removal therefrom. Theultra thin residue 82 may have a greatly varying thickness; however, inthe preferred embodiment residue 82 has a thickness 84 (which is showngreatly exaggerated for illustrative purposes in FIG. 7B) sufficient toenhance the corrosion resistance of the laser removed metal tube outersurface circumference 86 such that the laser removed metal tube outersurface circumference 86 improves its corrosion resistance significantlyover an outer surface circumference 86 having no polymeric layer 24 andno residue 82 thereon.

In the preferred embodiment, the laser removed metal tube outer surfacecircumference 86 passes up to about 1100 hours of Standard Method ofSalt Spray (Fog) Test ASTM B 117-73 before forming red rust builduplarger than about 1 mm (0.04") in diameter. A metal tube 28 having acorrosion resistant coating layer 30 without any polymeric layer 24 atall thereon can only pass up to between about 600 and about 800 hours ofthe test; whereas a metal tube 28 with corrosion resistant layer 30 anda polymeric layer 24 comprising one or multiple individual polymericlayers passes between up to about 5000 to 8000 or more hours beforeforming red rust buildup larger than about 1 mm (0.04") in diameter.Thus, the ultra thin polymeric residue 82 provides intermediateprotection between a tube 28 having no polymeric layer 24 and a metaltube 28 having a full polymeric layer 24 thereon.

As described in more detailed hereinbelow, polymeric layer 24, which maycomprise one or multiple individual polymeric layers, may have a varyingthickness 88. However, in the preferred embodiment, this thickness 88ranges between about 170 microns (0.0068") and about 202 microns(0.0081").

Due to the rotation of the C-shaped housing 46 and generally ellipticalcross-sectionally shaped laser beam 34 emitted therefrom rotating 360°about end 60 of multi-layer tube 22, the polymeric layer portion removal36 may be accomplished quickly, without rotating the tube 22, and in asingle pass. The cycle time for removal has a time ranging between about1 second and about 4 seconds. However, in the preferred embodiment, thepolymeric layer portion 36 removal is accomplished in approximately 3.5seconds.

The C-shaped housing 46, and consequently the laser beam 32 emittedthrough exit 52 may move from end 60 axially inward to about 3 inches;however, in the preferred embodiment, the C-shaped housing 46 does notsubstantially move axially with respect to tube 22, but rather movesrotationally thereabout. This is advantageous in that, among otheradvantages, it allows for a faster cycle time. Further, since metal tube22 in the preferred embodiment is a fixed, non-rotating workpiece, theelectro-optical process of polymeric layer portion 36 removal accordingto the present invention is less costly, more efficient, simpler tooperate, and lends ease in manufacturing. As a specific example of oneof the many advantages, the non-rotation of the tube 22 aids inmaintaining polymeric layer coating integrity. This is due to the factthat, when rotating a tube 22 which may have a degree of bowing to it,and which rotation may cause considerable vibration in the tube nuts,the polymeric coating could possibly be damaged.

The method of the present invention has particular use for high pressurefluid conduits having two ends 60', 60", with the polymeric layerportion 36 removed from each end 60', 60". The method may furthercomprise the step of endforming each of the conduit two ends 60', 60"into either an SAE-type double or inverted flare 90, as shown in FIG. 8in an appropriate tube nut 98; or an ISO-type annularly protruding flare92, as shown in FIG. 9 in an appropriate tube nut 99. Such endforminghas particular use to prepare multi-layer tubing for brakelineconnectors. Examples of suitable endforming apparatus may be found inU.S. Pat. Nos. 5,529,349 and 5,489,127. It is to be understood that theabove description of SAE and ISO enforms are exemplary, and that themethod of the present invention may be applicable to prepare tubing 22for many other forming and/or endforming operations.

As shown, each of the flares 90, 92 is formed approximately where thepolymeric layer portion 36 is removed. The center of radius on the SAEendform is designated 89; and the center of radius on the ISO endform isdesignated 93. In the preferred embodiment, the polymeric layer 24 isremoved to within this range. For a 3/16" tube size, the length of thecenters 89, 93 of radius is approximately 0.8 mm. As can be seen, thesmoothly tapered transition portion 74 covers a portion of the backsurfaces of the flares 90, 92. The transition portion 74 thereby leavesno blunt or rough edges to catch on bushings, tooling and/or connectionsand the like when the tube 22 is inserted therein and/or therethrough.

The metal multi-layer tube 22 may be particularly advantageous as atleast one of a brakeline, a vacuum line, a transmission oil cooler line,a vapor return line, or a fuel line. In addition to any otherapplications discussed further hereinbelow, tube 22 may also haveapplication in other areas.

The method of the present invention may remove one or more polymericlayers from a multi-layer tube 22. It is to be understood that corrosionresistant layer 30 on metal tube 28 of multi-layer tube 22 is optional.Further, if multi-layer tube 22 does have a corrosion resistant layer30, there may or may not be a surface treatment layer bonded thereto;ie. the surface treatment layer is also optional.

In the preferred embodiment, the tube 22 is hand-fed intoelectro-optical removal system 10; however, it is to be understood thatsystem 10 of the present invention may easily be adaptable to a morecomplex progressive/transfer machine, where system 10 may become one ofmany stations. The present system 10 strips one end 60, and can beadapted for two ends by splitting the beam, energizing one end at atime. However, it is to be understood that, as mentioned above, thepresent invention may easily be adaptable to a more complex machinehaving the capability of stripping two ends 60', 60" simultaneously.Still further, the present invention may be adaptable to a machinehaving the capability of impinging all circumferential surfaces of oneor both tube ends 60 simultaneously without rotation of the beamdelivery system 38. Yet still further, the present invention may beadaptable to a machine wherein the tube 22 is rotated, with or withoutrotation of the beam delivery system 38.

The polymeric layers may be applied by any or all of the followingexemplary, non-limitative methods: extrusion, flow coating,electrostatic spray painting, electrostatic powder coating, or shrinkfitting.

It is to be further understood that any or all of the variationsregarding the corrosion resistant coatings, surface treatment layers,and one or multiple polymeric layers, as well as methods for applyingthe same onto the metal tube 28, as described in further detailhereinbelow, may be suitable in the electro-optical system of thepresent invention for removing a plastic layer 24 from the outer surface26 of a metal tube 28.

Further details on the method for preparing the multi-layer tube 22appear hereinbelow. Corrosion can be minimized by various methods, forexample, by the use of a coating of protective metal such as zinc, tin,lead, nickel or copper; by the production of oxide, phosphate or similarcoatings on iron and steel surfaces; by the application of protectivepaints; and by rendering the surface of the metal passive. Galvanizingzinc is applied to metal surfaces by dipping into a bath of molten zinc,by electrodeposition, or by metal spraying.

In the hot process, after being thoroughly cleaned, the articles aredipped into a bath of molten zinc. The bath must be maintained at atemperature somewhat higher than the melting point of zinc. The portionof the zinc surface through which the material to be coated enters thezinc bath is kept covered with a flux; ammonium chloride and zincchloride are widely used for this. The process is used almostexclusively for sheet, pipe and wire. One or two percent tin is oftenadded in the coating of sheets in order to obtain a very uniform coatingand to improve the surface appearance. A coating applied by hot dippingnever consists of a simple layer of zinc. It is always of a compositenature, the layer adjacent to the base metal consisting of zinc-ironalloys. This layer is relatively brittle and, thereby, imposes somelimitations on hot-dipped galvanized materials for certain uses. Acoating of 1 oz/ft² (305 g/m²) of exposed surface is considered verysuitable for most conditions of service.

The electrolytic or cold process consists in setting up the articles tobe coated as cathodes and an electrolytic bath of soluble zinc salts,the anode being metallic zinc. The article to be coated being connectedto the cathode of the system. Both the acid sulfate and the cyanide bathare used. The high ductility of the pure zinc coating obtained is theoutstanding feature of such a coating. The ease of control of theuniformity and thickness is also advantageous.

A phosphate coating, in itself, forms only a very slight degree ofprotection against corrosion. Coatings of this kind are not suitable forsevere outdoor service. Phosphating a steel surface is an excellentmethod of priming prior to subsequent painting or lacquering. Thephosphate can be electrolytically applied, or can be applied byspraying. The phosphate treatment is also applicable to zinc surfaces.

The multi-layer tubing 22 according to the present invention includes ametal tube or pipe 28. The metal tube 28 may be welded steel tube,brazed steel tube, aluminum, copper or stainless steel. The process ofthe present invention is capable of applying a multi-layer coating overany rigid or semi-rigid tubular material. Of particular interest in thepresent invention, is the mechanical durability and corrosion resistanceadvantage obtained with carbon steel in either a welded single wall orbrazed double wall form of tube or piping. Application of multi-layercoatings on other materials may be of a decorative nature with someprotection also being obtained, for example improved chemical resistanceof the outer shell of the multi-layer coating over the underlying rigidor semi-rigid tubular material.

Referring now to FIG. 10, the metal tubing 28 is pretreated as requiredthrough various clean and rinse stages 100. In addition, the pretreatingof the metal surface may also include pickling to remove oxides and toimprove the metal surface for deposition of a metal based coating, suchas a zinc based coating that is applied by hot dip galvanization,sometimes referred to as the "hot process" as previously described, orthe preferred method of electrolytic bath coating or plating sometimesreferred to as the "electrolytic or cold process" as previouslydescribed. In the alternative, previously pretreated metal tubing 28 maybe supplied to the zinc based coating process step 102 according to thepresent invention, or a previously zinc base coated metal tubing 28 maybe supplied to the surface treating step 104 of the process according tothe present invention. In either case, metal tubing 28 with a zinc basedcoating applied thereon in a range of 0.4 to 1.0 mil is either producedor supplied for subsequent treating as will be disclosed hereinafteraccording to the present invention.

The external surface of the zinc based coating is treated to seal thezinc based coating to prolong its corrosion resistance and to provide asuitable surface for application of and bonding to extruded multiplelayers of plastic to be subsequently supplied. The surface treatment ofthe zinc based coating is at least one of the surface sealing treatmentsselected from the group of a phosphate coating, a chromate coatingincluding the clear, yellow and green versions, a zinc-aluminum alloycoating, and combinations thereof. A suitable zinc-aluminum alloy andcoating is described in U.S. Pat. No. 4,448,748 which is incorporatedherein by reference, and ASTM Designation: B750-88 provides a standardspecification for zinc-5% aluminum-mischmetal alloy in ingot formhot-dip coatings, which is also incorporated herein by reference. Metaltubing pretreatment prior to plastic application can includecombinations such as zinc-aluminum alloy with a phosphate coating and achromate coating, zinc plate with a chromate coating, zinc plate with aphosphate coating and a chromate coating, galvanized zinc with aphosphate coating and/or a chromate coating, zinc-nickel alloy platewith a phosphate coating and/or a chromate coating, zinc-cobalt alloywith a phosphate coating and/or a chromate coating, a chromate coatingof the clear, yellow and green versions, and combinations thereof. Thepretreatment of the metal surface prior to the zinc base coating caninclude sand, shot or bead blasting, or other means of abrading thesurface to roughen it, or detergent cleaning with rinse and acidpickling followed by a rinse. Any suitable surface abrading or etchingprocess, either chemical or mechanical, may be used as a pretreatmentprior to any other surface treatment and/or prior to extruding plasticonto the metal surface. The chromate coating can be applied as a washhaving essentially no remaining weight. The zinc-aluminum alloy coatingcan be applied with a weight selected in a range of between 36 to 95g/m² inclusive, and with a preferred weight range of between 75 to 80g/m² inclusive and a most preferred weight of 78 g/m². The phosphatecoating can be applied with a weight in the range of between 120 to 250mg/ft² (1.292 to 2.691 g/m²) inclusive. The zinc based coating on themetal surface is preferably a weight in the range of between 13 to 35microns inclusive.

Various combinations of multi-layer tubing 22 according to the presentinvention have been prepared with metal tube 28 having a 3/16 inchdiameter brazed tube, or 5/16 inch and 3/8 inch diameter welded steeltube. The process according to the present invention is not sizedependent, and therefore it is anticipated that other sizes, includingsmaller sizes and larger sizes, of metal tube 22 can be processedaccording to the present invention.

The zinc-aluminum galvanizing alloy or coating preferably contains fromabout 85% to 97% zinc, from about 4% to 15% aluminum and at least about5 ppm mischmetal (a variety of known rare earth containing alloys).

After treating the surface of the zinc based coating or layer 23 withthe surface treatment layer 25, multiple plastic layers are extruded onthe treated surface 25 of the zinc based layer 23 in step 106. In thealternative, multiple plastic layers can be extruded on to the externalsurface of the metal tube 28 without pretreatment. In either case, themultiple plastic layers preferably include at least an alloy or bondinglayer, referred to herein as a first layer 27 formed on top of thetreated surface layer 25 and an external shell or second layer 29exposed to the outside environment. An optional intermediate or thirdlayer 31 may be provided between the first layer 27 and the second layer29 and may include one or more sublayers of plastic materials. Prior toextruding the multiple plastic layers onto the treated surface 25, themetal tube 28 is preheated to temperatures in the range of between 177°C. to 232° C. (350° F. to 450° F.) inclusive, with a preferred range ofbetween 204° C. to 232° C. (400° F. to 450° F.) inclusive. The multiplelayers of extruded plastic form a coating over the treated surface 25with an overall thickness in a range of between 75 to 300 microns (3 to12 mils), with a preferred range of between 125 to 250 microns (5 to 10mils). Individual plastic layers can be applied with a thickness in arange of between 10 to 250 microns (0.3 to 10 mils) inclusive, with apreferred range of between 125 to 250 microns (5 to 10 mils) inclusive.

Referring now to FIG. 11, a more detailed flow diagram of a processaccording to the present invention is depicted. The tubing 28 aspreviously described is subjected to a clean and rinse step 108 followedby a pickling process step 110 to remove oxides and to improve theexternal metal surface for subsequent flash plating. After the picklingstep 110, the metal tubing 28 is subjected to a rinse step 112. Theelectroflux and flash plate with zinc step 114 then applies the zincbased layer of a thickness in the range of 0.4 to 1.0 mil inclusive. Azinc-aluminum alloy coating is then applied to the external surface ofthe zinc based layer. A suitable zinc-alloy coating is commerciallyavailable under the tradename GALFAN from Eastern Alloys, Inc. ofMaybrook, N.Y. The sealing step 116, of applying GALFAN whilecontrolling the thickness in a range of 36 to 95 g/m² with a mostpreferred thickness of 78 g/m², is followed by a water quench step 118to bring the tubing 28 back to ambient temperature, followed by a rinsestep 120. It is to be understood that any of the quenching steps asdiscussed herein may be performed using any suitable material orprocess. Step 122 provides for a phosphate surface to be applied to theexternal surface of the GALFAN coating for improved adhesion ofsubsequent layers. A rinse step 124 follows the phosphating step 122.The application of a chromate coating occurs in step 126 to seal thephosphate surface applied in step 122. The phosphate surface ispreferably applied with a thickness in the range of 120 to 250 mg/ft²(1.292 to 2.691 g/m²), while the chromate coating may be applied as awash having essentially no remaining weight on the tubing uponcompletion. After the chromate wash step 126, the multiple layers ofplastic are extruded onto the metal tubing 28 in step 128. Preferably,the tubing has been heated in a range of between 375 to 450° F.inclusive with a preferred temperature of 425° F. prior to theapplication of the multiple layers of plastic in step 128. Aconventional mechanical applicator or extrusion head is used forcoextruding the multiple layers of plastic simultaneously onto thesurface of the preheated metal tube 28. In the preferred configuration,vacuum is applied to the head of the applicator to pull the plasticmaterial down onto the surface of the preheated tube 28. The vacuumapplied is preferably in the range of 1 inch to 22 inches of water(where 28 inches of water is equal to atmospheric pressure), with apreferred vacuum pressure of 10 inches of water. After extrusion of themultiple layers of plastic in step 128, the tubing 28 is subjected to aquench in step 130, which can be a water quench, oil quench or othermaterial quench as required, and is thereafter coiled or cut to finishedlength in step 132.

In lieu of coextrusion, the process could also be carried out as across-head application wherein the layers are applied synchronouslyinstead of simultaneously. However, this process is not as preferred asthe coextrusion, in that there is a greater likelihood of loss ofbonding efficiency and bonding properties, and there tends to be lesscontrol over layer thicknesses.

Referring now to FIG. 12, a detailed flow diagram of a process accordingto the present invention is disclosed. In step 134, the tubing issubjected to a hydro-mechanical cleaning with detergent additive. Instep 136, the tubing is driven by a first drive unit in a continuousprocess through the following steps described below. The metal tubing 28is driven through step 138 which includes an electro-cleaning processusing sodium hydroxide. After the electro-cleaning process in step 138,the metal tubing 28 passes through a rinse step 140. A pickling step 142using hydrochloric acid is followed by another rinse step 144. Thetubing engages contact #1 cathode at step 146 and passes through a zincchloride bath at zinc plating cell #1 in step 148. Thereafter, the metaltubing 28 engages contact #2 cathode at step 150 and passes through azinc chloride bath and zinc plating cell #2 at step 152. At step 154,the metal tubing 28 is subjected to drying, where flux may be applied ifappropriate. A zinc-alloy coating is applied in step 156. As previouslydescribed, a suitable zinc-alloy coating is available under thetradename GALFAN from Eastern Alloys, Inc. located in Maybrook, N.Y.

The metal tubing 28 then passes through a gas mist cooler at step 158,followed by a quench at step 160 and rinse with conditioner at step 162.The metal tubing then passes through a phosphoric acid mix where a zincphosphate coating is applied at step 164 followed by a rinse at step166. Thereafter, the metal tubing 28 passes through a chromic acid mixwhere a chromate rinse at step 168 seals the phosphate layer followed bydrying and heating at step 170. After heating to the desired temperaturerange, the metal tubing 28 passes through an extrusion head forapplication of multiple plastic layers to the outer chromate sealingsurface in step 172. Preferably, the vacuum is applied to the extrusionhead in order to draw the plastic down into intimate contact with thechromate surface. Suitable plastic materials for the multiple layersapplied to the metal tubing 28 are described in greater detail hereinbelow. Following the extrusion process step 172, the multi-layer tubing22 is subjected to a water quench at 174 followed by passing throughdrive #2 which places the tubing in tension at step 176 followed finallyby a cutoff step 178 where the tubing is cut to the appropriate lengthor coiled as desired.

Referring now to FIG. 6, the multi-layer tube of the present inventionis designated generally as 22. Multi-layer tube 22 comprises a tube orpipe 28 having an outer surface 26. Tube 28 may be formed in anyconventional manner and of any suitable material. For example, tube 28may be a welded single wall steel tube, a brazed double wall steel tube,etc. Further, aluminum, stainless steel and the like also may be used.Yet still further, tube 28 may be formed from any rigid or semi-rigidtubular material. Tube 28 may be of circular cross section as shown,however, it is to be understood that tube 28 may be formed of anysuitable size and/or shape, including square, rectangular and othergeometric configurations.

A suitable corrosion resistant layer 30 may be bonded to metal tubeouter surface 26. In the preferred embodiment, corrosion resistant layer30 comprises a zinc layer 23 bonded to the metal tube outer surface 26.It is to be understood that any suitable zinc layer 23 may be used inaccord with the present invention. However, in the preferred embodiment,the zinc layer is selected from the group consisting of zinc plating,zinc nickel alloys, zinc cobalt alloys, zinc aluminum alloys, andmixtures thereof.

A surface treatment layer 25 is bonded to the zinc layer 23. Anysuitable surface treatment layer 25 may be used. However, in thepreferred embodiment, surface treatment layer 25 is selected from thegroup consisting of a zinc/aluminum/rare earth alloy, phosphate,chromate, and mixtures thereof.

The phosphate and/or chromate may be applied in any suitable manner. Inthe preferred embodiment, a hot phosphoric acid is used. Without beingbound to any theory, it is believed that this acid etches into the metalsurface, leaving a phosphate crystalline structure in the metal, whichstructure aids in subsequent adhesion of polymeric materials. Overelectroplating, a wet bath chromate may be used, after which the metalis rinsed well. Chromium oxides are left on the metal, which arebelieved to aid in corrosion resistance, and which, although optional,are further believed to enhance the advantageous properties of thephosphate. Over the zinc/aluminum/rare earth alloy treatment, a drychromate may be used which does not require subsequent rinsing.

The zinc/aluminum/rare earth alloy used is preferably GALFAN,commercially available from Eastern Alloys, Inc. in Maybrook, N.Y.;licensed from the International Lead Zinc Research Organization, Inc.located in New York, N.Y.; and described in U.S. Pat. No. 4,448,748,discussed more fully above. Particularly preferred is the combination ofthe GALFAN with the phosphate, or the GALFAN with the phosphate andchromate. Without being bound to any theory, it is believed that eitherof these two combinations for the surface treatment layer 25 areparticularly advantageous and useful in the present invention.

It is to be understood that the zinc layer 23 and/or surface treatmentlayer 25 may be optional components of the present invention. Variouspolymeric compositions may be applied directly to a bare metal surface,especially for decorative purposes. Further, it is contemplated thatvarious polymeric compounds and/or blends, including those containingsuitable ionomers, may substantially bond to an untreated metal surface,thereby giving the numerous corrosion and abrasion resistant propertiesenumerated herein.

A first polymeric layer 27 is bonded to the surface treatment layer 25.It is to be understood that any suitable polymeric layer may be usedwhich suitably bonds to the surface treatment layer 25, and in turn,suitably bonds to subsequent polymeric layers, if any. In the preferredembodiment, the first polymeric layer 27 is selected from the groupconsisting of thermoplastic elastomers, ionomers, nylons,fluoropolymers, and mixtures thereof.

A second polymeric layer 29 may be bonded to the first polymeric layer27, as shown in FIGS. 7A and 7B. It is to be understood that anysuitable polymeric layer may be used which suitably bonds to first layer27, and which provides suitable mechanical and chemical corrosionresistance. In the preferred embodiment, the second polymeric layer 29is selected from the group consisting of nylons, thermoplasticelastomers, fluoropolymers, and mixtures thereof.

The multi-layer tube 22 may further comprise a third polymeric layer 31interposed between, and bonded to the first and second polymeric layers.It is to be understood that any suitable polymeric layer may be usedwhich suitably bonds to first layer 27 and to the second layer 29 andwhich may optionally provide suitable cushioning, if desired. In thepreferred embodiment, the third polymeric layer 31 is selected from thegroup consisting of ionomers, nylons, ethylene vinyl alcohol,polyolefins, and mixtures thereof.

It is to be understood that any or all of the three layers, 27, 29, 31may include multiple sublayers (not shown). Further, it is to beunderstood that each of the layers and/or sublayers may be formed from asingle compound listed in the relevant group, or from a combinationthereof. Still further, it is to be understood that each of thelayers/sublayers may be comprised of the same material. The thickness ofthe combined polymer layers can be as little as 0.004 inch, and can bemade even thinner. Successful coatings have been applied having combinedpolymer layer thicknesses of 0.004 inch, 0.005 inch, 0.006 inch, 0.007inch, 0.009 inch and 0.010 inch, with a preferred range of 0.005 inch to0.010 inch.

Examples of suitable compounds for each of the layers will be describedhereinafter.

One of the advantages of the present invention is that a chemical ormechanical bond is formed between all the layers. It is believed thatgood bonding prevents moisture buildup beneath the layers, which buildupgreatly increases the likelihood of corrosion.

An ionomer is a thermoplastic polymer that is ionically crosslinked.Ionomer technology entails the reaction of copolymers to form bondsbetween the acid groups within a chain and between neighboring chains.Ionomers generally consist of an organic backbone bearing a smallproportion of ionizable functional groups. The organic backbones aretypically hydrocarbon or fluorocarbon polymers and the ionizablefunctional groups are generally carboxylic or sulfonic acid groups.These functional groups, which generally reside on no more than about10% of the monomer units in the polymer, may be neutralized, for examplewith sodium or zinc ions.

The presence of these ionic groups gives the polymer greater mechanicalstrength and chemical resistance than it might otherwise have. Theionomer is resistant to dissolution in many solvents because of itsunconventional chemical character, often being too ionic to dissolve innon-polar solvents and too organic to dissolve in polar solvents. Avariety of ionomers include copolymers of: styrene with acrylic acid;ethyl acrylate with methacrylic acid; and ethylene with methacrylicacid.

The presence of ions in an otherwise organic matrix is generally notthermodynamically stable. As a result, these materials undergo slightphase separation in which the ions cluster together in aggregates. Theseionic clusters are quite stable and may contain several water moleculesaround each metal ion. They act partly as crosslinks and partly asreinforcing filler, which may provide the greater mechanical strengththat ionomers exhibit.

A further general discussion of ionomers can be found in The Chemistryof Polymers by John W. Nicholson, published by the Royal Society ofChemistry, Thomas Graham House, Cambridge England (1991), pp. 147-149.

It is to be understood that any suitable ionomer resin may be used inthe present invention, which suitable ionomer resin has substantiallysimilar physical properties and performs in a substantially similarmanner to the ionomers disclosed herein. Without being bound to anytheory, it is believed that the presence of the ionomer may greatlyenhance the excellent bonding formed between the metal surfaces 26, 23,25 and the subsequent polymer layer(s). In the preferred embodiment,SURLYN ionomer resins are used. Other suitable ionomers are commerciallyavailable under the tradename IOTEK from Exxon Chemical Co. located inHouston, Tex.

SURLYN® is an ionomer resin commercially available from E. I. DuPont deNemours & Co., located in Wilmington, Del. The chemical name of SURLYNis ethylene methacrylic acid copolymer--partial metal salt. Its chemicalformula is represented as [(CH₂ --CH₂)_(x) (CH₂ CCH₃ COO⁻ M⁺)_(y) ]_(n).In the SURLYN Ionomer Resins, ethylene and methacrylic acid copolymersare partially reacted with metallic salts.

General physical characteristics of the SURLYN Resins include a meltingpoint between about 80° C. and about 100° C. The resins are insoluble inwater and are supplied in the form of solid white pellets. The compoundshave a mild methacrylic acid odor. SURLYN ionomer resins have excellentimpact toughness, flexibility, cut and abrasion resistance, lowtemperature performance and long term durability, especially at specificgravities of less than one. The SURLYN Ionomer Resins have roomtemperature tensile impact properties ranging from about 730 to about1325 kJ/m² (345 to 630 ft-lb/in²). This impact performance does not dropsubstantially with temperature, in that the compound can offer tensileimpact as high as 1190 kJ/m² (565 ft-lb/in²) at -40° C. Various gradesof the SURLYN Ionomer Resins have a notched Izod rating as high as 853J/m (16 ft-lb/in). The SURLYN Resins are also highly resistant tochemical attack and permeation by liquids. They have high melt strengthsand contain no plasticizers. Ionomers adhere well to metals and tofinishes of epoxy and urethane. The resins range in specific gravityfrom 0.94 to 0.97 g/cm³.

Of the SURLYN Resin grades, a preferable grade is SURLYN 8528. Alsopreferred is SURLYN 8527, which has the same physical properties as8528, but offers greater clarity. It is to be understood that any gradeof SURLYN is contemplated as being of use in the present invention,however, the grade of SURLYN should not possess a melt viscosity whichwould be so high as to hinder the advantageous functioning of thepresent invention. Typical physical properties of SURLYN 8528 will bediscussed hereinafter.

SURLYN 8528 has excellent abrasion and cut resistance. Its processingtemperature is about 450° F. (232° C.). Its density is 58.6 lb/ft³ (0.94g/cm³). Its brittle temperature is -139° F. (-95° C.). Its volumeresistivity is 1.00×10¹⁶ Ohm cm. Its dielectric constant is 2.40×10⁶ Hz.

The SURLYN 8528 toughness properties include tensile impact at 23° C.(73° F.) of 1160 kJ/m² (550 ft-lbf/in²). This is as found under ASTMMethod D-1822S. Another toughness property is measured by the Notchedizod test. This particular test is not as relevant for tubing--a morepreferred test is a Cold Temperature Impact Test as described inPerformance Requirements paragraph 9.11 in SAE Standard J844 as revisedin June of 1990. However, the SURLYN 8528 Notched izod is 610 J/m (11.4ft-lb per inch of notch) under ASTM Method D-256.

For low temperature toughness, the SURLYN 8528 tensile impact at -40° C.(-40° F.) is 935 kJ/m² (445 ft-lbf/in²) under ASTM Method D-1822S.

Durability is measured by abrasion resistance under ASTM Method D-1630.The SURLYN 8528 resistance is 600 under the NBS index. For claritymeasurement, the haze at 0.64 cm (0.25 in) under ASTM Method D-1003A is6%. The specific gravity under ASTM Method D-792 is 0.94 g/cm³.

The stiffness and other mechanical properties of SURLYN 8528 are givenby the following. The flexural modulus at 23° C. (73° F.) under ASTMMethod D-790 is 220 MPa (32 kpsi). The tensile strength, yield strengthand elongation are measured on Type IV bars, compression molded, with across head speed of 5.0 cm/min (2 in/min). All three of these propertiesare measured by ASTM Method D-638. The tensile strength is 29 MPa (4.2kpsi); the yield strength is 12.4 MPa (1.8 kpsi) and the elongation is450%. The Ross Flex was tested on compression molded samples 3.2 mmthick, pierced 2.5 mm wide, under ASTM Method D-1052. Pierced at 23° C.(73° F.), the Ross Flex is 3000 cycles to failure; and pierced at -29°C. (-20° F.) is less than 100 cycles to failure. The MIT flex is anaccelerated stress crack test on a strip 25 mil. thick, flexed through270° at 170 cycles per minute with one kilogram load in tension--#04head. This is a test developed by Dupont. The result on the SURLYN 8528was 2100 cycles to failure. The Shore D hardness is about 60 to 62.

General physical characteristics of SURLYN 8528 include cation type:sodium. The melt flow index, with the material dried 16 hours in avacuum oven at 63° C. (145° F.) under ASTM Method D-1238 was 1.3 g/10minutes. The area yield at 0.25 mm (0.10 in) was 4.2 m² /kg (20.1 ft²/lb).

Thermal characteristics include a heat deflection temperature at 455 kPa(66 psi) of about 44° C. to 51° C. (111° F. to 125° F.) under ASTMMethod D-648. The Vicat temperature under ASTM Method D-1525-70 Rate Bis 71° C. to 73° C. (159-163° F.). The melting point and freezing pointis determined by differential thermal analysis. The melting point is 94°C. to 96° C. (201° F. to 204° F.); and the freezing point is 75° C.(167° F.). The coefficient of thermal expansion from -20° C. to 32° C.under ASTM Method D-696 is 14×10⁻⁵ cm/cm/° C. The flammability underASTM Method D-635 is 22.9 mm/min (0.9 in/min); and the flammabilitypassed the Motor Vehicle Safety Standard 302. The thermal conductivityis 6.0×10⁻⁴ cal/cm² /sec/° C./cm. The specific heat at various degreeswill be given. At -20° C. (68° F.), mean: the specific heat is 0.43cal/gm/° C.; at 60° C. (140° F.), mean: the specific heat is 0.58cal/gm/° C.; at melting point, mean: the specific heat is 0.86 cal/gm/°C.; and at 150° C. (302° F.), mean: the specific heat is 0.55 cal/gm/°C.

The thermoplastic elastomers which can successfully be employed in thetubing 22 of the present invention are commercially available undertradenames such as: SANTOPRENE®, a thermoplastic rubber commerciallyavailable from Advanced Elastomer Systems of St. Louis, Mo.; KRATON®, athermoplastic rubber composed of a styrene-ethylene/butylene-styreneblock copolymer commercially available from Shell Chemical Co. ofHouston, Tex.; SARLINK, an oil resistant thermoplastic commerciallyavailable from Novacor Chemicals of Leominster, Mass.; and VICHEM, afamily of polyvinyl chloride compounds commercially available fromVichem Corporation of Allendale, Mich.

Of the various thermoplastic elastomers suitable in the presentinvention, HYTREL is a preferred compound. HYTREL is a thermoplasticelastomer commercially available from E. I. DuPont de Nemours & Co.,located in Wilmington, Del. It is contemplated that any grade of HYTRELis useful in the present invention, preferably such a grade whichpossesses a Shore D Hardness ranging between about 40 and about 55, andstill more preferably, one having a Shore D Hardness of about 40. Gradeshaving D40 (Shore) hardness include G-4074; G-4078; 4056; and 4059 FG.

The HYTREL grades listed above are polyester thermoplastic elastomers,and special features include excellent heat aging and oil (at hightemperatures) resistance; can be used in light colored products;excellent low temperature properties, fatigue, flex and creepresistance.

Principal properties of the HYTREL grades listed above are as follows.Melt flow (condition): between about 5.2 (E) and about 5.4 (E); about8.5 (L). Melting point: between about 298° F. and about 383° F. Density:between about 1.11 g/cm³ and about 1.18 g/cm³. Tensile strength, yield:between about 450 lb/in² and about 550 lb/in² (with 10% strain). Tensilestrength, break: between about 2.00×10³ lb/in² and about 4.05×10³lb/in². Elongation, break: between about 170% and about 600%. Flexuralmodulus: between about 8.00×10³ lb/in² and about 9.80×10³ lb/in². Izod,Notched, R.T.: about 999 ft-lb/in (no break). vicat Soft Point: betweenabout 226° F. and about 273° F. Water Absorption, 24 hour: between about0.60% and about 2.50%.

A suitable nylon material includes 12 carbon block polyamides, 11 carbonblock polyamides, and zinc chloride resistant 6 carbon block polyamides.Of these, Nylon 12 and zinc chloride resistant Nylon 6 are preferred.The 6-carbon block polyamide or Nylon 6 either inherently exhibits zincchloride resistance or contains sufficient quantities of modifyingagents to impart a level of zinc chloride resistance greater than orequal to that required by Performance Requirement 9.6 as outlined in SAEStandard J844 (Revised June 1990), i.e. non-reactivity after 200 hourimmersion in a 50% by weight zinc chloride solution. The Nylon 6 canalso be modified with various plasticizers, flame retardants and thelike in manners which would be known to one reasonably skilled in theart.

Suitable fluoropolymers may include polyvinylidine fluoride, polyvinylfluoride, ethylene tetrafluoroethylene, and mixtures thereof. Thematerial can also be a graft copolymer of the preceding materialstogether with a fluorine-containing polymer such as copolymers ofvinylidine fluoride and chlorotrifluoroethane. Suitable materialemployed may contain between about 60% and about 80% by weightpolyvinylidine difluoride. Materials so formed have a melting pointbetween about 200° C. and about 220° C. and a molding temperaturebetween about 210° C. and about 230° C. Further suitable fluoropolymersinclude: a copolymer of a vinyl fluoride and chlorotrifluoroethylene,the vinyl fluoride material selected from the group consisting ofpolyvinylidine fluoride, polyvinyl fluoride, and mixtures thereof; acopolymer of vinyl fluoride material and ethylene tetrafluoroethylene; anon-fluorinated elastomer, and mixtures thereof. The material of choiceexhibits an affinity to polymers employed in the first 27 second 29 orthird 31 layers, such as, for example, Nylon 12 or Nylon 6. Somesuitable fluoropolymers are commercially available under the tradename"ADEFLON A" from Atochem Inc. elf Aquitaine Group of Philadelphia, Pa.

Other suitable materials, especially useful in an interposed layer 31 orin sublayers of any of the three layers 27, 29, 31 include ethylenevinyl alcohol, selected from the group consisting of copolymers ofsubstituted or unsubstituted alkenes having less than four carbon atomsand vinyl alcohol, and mixtures thereof. Also useful are copolymers ofalkenes having less than four carbon atoms and vinyl acetate. Alsosuitable are polyolefin compounds, including, but not limited topolyethylene, low density polyethylene, and polypropylene.

The following is a brief description of the various exemplary,commercially available compounds described hereinabove. It is to beunderstood that these are examples of suitable compounds forillustrative purposes. Thus, it is to be further understood that othersuitable compounds are contemplated and are within the scope of thepresent invention.

SANTOPRENE®, commercially available from Advanced Elastomer Systems,L.P. of St. Louis, Mo. is a thermoplastic rubber FR grade. Aside fromthe thermoplastic rubber, it also contains antimony trioxide flameretardant, and may contain carbon black, CASE No. 1333-86-4. SANTOPRENE®thermoplastic rubber may react with strong oxidizing chemicals, and alsoreacts with acetal resins at temperatures of 425° F. and above,producing decomposition of the acetal resins, and formaldehyde as adecomposition product. Decomposition of halogenated polymers andphenolic resins may also be accelerated when they are in contact withSANTOPRENE® thermoplastic rubber at processing temperatures. Physicalcharacteristics of SANTOPRENE® include a slightly rubber-like odor, andthe appearance of black or natural (colorable) pellets. It is thermallystable to 500° F. The flash ignition temperature is greater than 650° F.by method ASTM-D 1929-77, and by the same method, self-ignitiontemperature is above 700° F. The typical specific gravity is 0.90 to1.28. The material has various hardnesses which are suitable in thepresent invention, however, in the preferred embodiment, the SANTOPRENE®thermoplastic rubber having an 80 Shore A hardness is utilized. TheSANTOPRENE® thermoplastic rubber is designed to offer fluid and oilresistance equivalent to that of conventional thermoset rubbers such asneoprene. The resistance of the SANTOPRENE® rubber grades to oils can beclassified by using the SAE J200/ASTM D2000 standard classificationsystem for rubber.

ADEFLON A is a polyvinylidene fluoride commercially available fromAtochem Inc. elf Aquitaine Group of Philadelphia, Pa. Its typical use isas a binding material for polyamides/polyvinylidene fluoride. Theproduct is stable under normal use conditions, and above 230° C., thereis a release of monomer traces. Physical properties include: at 20° C.the material is a granulated solid having a white/slightly yellow colorand no odor. The crystal melting point is 175° C., and beginning ofdecomposition is 230° C. In water at 20° C., the product is non-soluble.The density at 20° C. bulk is 1 to 1.1 g/cm³.

The Vichem Corporation vinyl compounds are polyvinyl chloride compoundscomposed of a vinyl resin and functioning additives. The ingredientsinclude a stabilizer, a resin CASE No. 75-01-4, a plasticizer CASE No.68515-49-1, an epoxy soya oil CASE No. 8013-07-8, a filler CASE No.1317-65-3 and carbon black CASE No. 1333-85-4. The specific gravity is1.35 and the compound has the appearance of pellets and has acharacteristically bland odor.

KRATON®, commercially available from Shell Chemical Co. of Houston,Tex., is a thermoplastic rubber having a specific gravity of 0.90 to1.90 and a hardness of 15 A to 60 D. The tensile strength is up to 2,500psi. The elongation is up to 750% and the tear strength is up to 750 pli(130 kN/m). The flex modulus is 750 to 100,000 psi. The servicetemperature is -70° C. to 150° C. The ozone resistance is excellent, UVresistance is excellent, fluid resistance is fair to excellent, andflame resistance is fair to excellent.

SARLINK is a thermoplastic elastomer commercially available from NovacorChemicals Inc. of Leominster, Mass. The specific gravity ranges from1.13 to 1.22. The modulus at 100% ranges between 260 and 570 psi. Thetensile strength ranges between 780 and 2,060 psi. The ultimateelongation ranges between about 345 and about 395%. The tear strengthranges between about 81 and about 196 pli. The tension set rangesbetween about 4 and 6%. It has excellent fluid resistance to acids andalkalis, aqueous solutions, organic solvents, petroleum oils and fuels,automotive fluids such as automatic transmission, power steering, etc.and industrial fluids. It has fair fluid resistance to automotive fluidssuch as hydraulic brake, lithium grease, antifreeze, etc. and poorresistance to organic solvents. The SARLINK product is a solid, blackpellet material with a mildly pungent odor. It is insoluble in water at20° C.

Another suitable fluoropolymer is KYNAR, commercially available fromAtochem Inc. elf Aquitaine Group of Philadelphia, Pa. KYNAR is avinylidene fluoride-hexafluoropropylene copolymer. Its chemical name is1-propene,1,1,2,3,3,3-hexafluoro-1,1-difluoroethene polymer. Its meltingpoint is 155°-160° C. Its specific gravity is 1.77-1.79 at 23° C. Itappears translucent and has no odor.

Another suitable fluoropolymer is CEFRAL SOFT XUA-2U, commerciallyavailable from Central Glass Company, Ltd., Chiyodaku, Tokyo, Japan is acopolymer containing 40% vinylidene fluoride-chlorotrifluoroethylenecopolymer, 30% polyvinylidene fluoride and 30% Nylon 12. The materialhas a specific gravity of 1.45 at 23° C., a melting point of 173° C. anda mold temperature of 220° F. The material has an elongation at break of478% and a tensile strength of 430 Kgf/cm².

Yet another suitable fluoropolymer is TEFZEL, which is commerciallyavailable from DuPont Polymers, Specialty Polymer Division, Wilmington,Del. The material designates a family of ethylene tetrafluoroethylenefluoropolymers having various commercial grades. The material has amelting point between 255° C. and 280° C. as determined by ASTM methodDTA D3418. The specific gravity for the material is between 1.70 and1.72 as determined by ASTM method D792. Impact strength for the materialat -65° F. is between 2.0 ft-lbs/inch and 3.5 ft-lbs/inch as determinedby ASTM method D256, commonly referred to as Notched Izod ImpactStrength. The hardness durometer as determined by ASTM method D2240 forall grades of TEFZEL is D70. Tensile strength at 73° F. is between 5,500psi and 7,000 psi. TEFZEL was first introduced in 1970 havingoutstanding mechanical strength, high temperature and corrosionresistance. The material is available in three production grades, TEFZEL200, TEFZEL 210 and TEFZEL 280 which can be applied in the presentinvention. Ultimate elongation at break is between 150% and 300%,depending on the grade as determined by ASTM method D638.

The multi-layer tube 22 may have the first polymeric layer 27 consistingessentially of an ionomer and a nylon, such as ethylene methacrylic acidcopolymer--partial metal salt, and Nylon 12. This may be in any suitablepercent composition and may have any additional suitable additives. Inthe preferred embodiment, this percent composition ratio is betweenabout 10% and about 70% ethylene methacrylic acid copolymer--partialmetal salt, and between about 90% and about 30% Nylon 12. Morepreferably, this percent composition ratio is between about 40% andabout 60% ethylene methacrylic acid copolymer--partial metal salt, andbetween about 60% and about 40% Nylon 12.

The second polymeric layer 29 may consist essentially of a nylon. In thepreferred embodiment, this layer is Nylon 12.

Third layer 31 may be any of the suitable materials listed hereinabove.In an alternate preferred embodiment, this third layer 31 may be a"regrind" or "recycle" of the suitable polymeric materials enumeratedabove. It is to be understood that the definition of "regrind" or"recycled" material as used herein comprises any generation of "regrind"or "recycled" material which substantially possesses between about 65%and about 95% (or higher) of each of the cold temperature impact,viscosity and elongation properties of the virgin material; morepreferably, possesses between about 80% and 95%, and still morepreferably possesses between about 90% and 95%. However, it is to beunderstood that any suitable regrind which performs in the desiredmanner in the present invention is contemplated and may successfully beused herein. If such a "regrind" is used as third layer 31, it ispreferred that a virgin material be used as second (outer) layer 29.

Among some advantages of regrind material is that it is believed thatthe regrind is a lower viscosity material, which may enhance extrusioncapabilities. Further, regrind is more rigid than virgin material,thereby improving penetration resistance as well as resistance to otherdamaging wear characteristics.

To further illustrate the composition, the following examples are given.It is to be understood that these examples are provided for illustrativepurposes and are not to be construed as limiting the scope of thepresent invention.

EXAMPLE I

A 3/16 inch brazed steel tube had a GALFAN coating of 78 g/m² and aphosphate coating of 120-250 mg/ft². Applied thereto was a coating of0.005 inch to 0.010 inch Nylon 12. In a subsequent test, two layers ofNylon 12 having a total thickness between about 0.005 inch to 0.010 inchwere also applied. In another subsequent test, three layers of Nylon 12having a total thickness between about 0.005 inch to 0.010 inch werealso applied. In all three tests, the Nylon 12 formed a tough, abrasionand corrosion resistant coating which strongly adhered to the steel tubeouter surface.

EXAMPLE II

A 3/16 inch brazed steel tube had a GALFAN and phosphate coating asnoted in Example I, with an additional chromate wash, with the chromatewash having essentially no remaining weight. A first polymeric layer wasapplied to the surface treated tube, the layer consisting essentially of20% SURLYN 8528 and 80% Nylon 12. Two subsequent layers of Nylon 12 werethen applied. The total thickness of the three polymeric layers rangedbetween about 0.005 inch to 0.010 inch. The three layers formed a tough,abrasion and corrosion resistant coating which appeared to more stronglyadhere to the steel tube outer surface than did the application of Nylon12 as outlined in Example I.

EXAMPLE III

A 3/16 inch brazed steel tube has a GALFAN coating of between about36-95 g/m² and a phosphate coating of 120-250 mg/ft². A first layer ofSURLYN 8528 is applied thereto. In a subsequent layer, 20% SURLYN 8528and 80% Nylon 12 is applied. As an outer layer, Nylon 12 is applied. Thethree layers form a tough, abrasion and corrosion resistant coatingwhich strongly adheres to the steel tube outer surface.

EXAMPLE IV

A 3/16 inch brazed steel tube has a GALFAN coating of between about36-95 g/m² and a phosphate coating of 120-250 mg/ft². A first layer of20% SURLYN 8528 and 80% Nylon 12 is applied. A second layer of Nylon 6(zinc chloride resistant) is applied. A third layer of ethylene vinylalcohol is applied. A fourth layer of Nylon 6 (zinc chloride resistant)is applied. A fifth layer of a blend of Nylon 6 (zinc chlorideresistant) and Nylon 12 is applied. A sixth, outer layer of Nylon 12 isapplied. The six layers form a tough, abrasion and corrosion resistantcoating which strongly adheres to the steel tube outer surface.

EXAMPLE V

Each of the tests contained in the above Examples are also performed on5/16 inch welded steel tubes and 3/8 inch welded steel tubes, and givethe same results noted above.

EXAMPLE VI

A 5/16 inch welded steel tube had no surface treatment. Applied theretowas a coating of 0.005 inch to 0.010 inch Nylon 12. In a subsequenttest, two layers of Nylon 12 having a total thickness between about0.005 inch to 0.010 inch were also applied. In another subsequent test,three layers of Nylon 12 having a total thickness between about 0.005inch to 0.010 inch were also applied. In all three tests, the Nylon 12formed a decorative coating surrounding the steel tube outer surface.

EXAMPLE VII

3/16" and 1/4" brazed steel tubing were prepared according to Example I,where two layers of Nylon 12 having a total thickness between about0.005 inch to 0.010 inch were applied to each of the tubes. Each of the3/16" and 1/4" tube ends were placed through a 0.213" diameter entrybushing and a 0.275" diameter entry bushing, respectively, into aWD-1LTC-200 (200 Watt) Laser Wire Stripper modified with the defocusinglens discussed hereinabove. The laser beam was activated to impinge theouter circumference of the end of each of the non-rotating tubes, and,in 3.5 seconds, a length of 6 mm of both layers of Nylon 12 was removedfrom the outer circumference of the ends, leaving a tapered transitionportion having a length of 1.27 mm. Under electron beam microscopeanalysis, it was determined that the GALFAN/phosphate coating wasundamaged. The tubes had a satisfactory amount of Nylon 12 removed toprepare them for subsequent SAE or ISO endforming.

EXAMPLE VIII

3/16" and 1/4" tubing were prepared as in Example VII. An ultra thin,shiny polymeric residue was detected on the laser removed surface ofeach tube. The laser removed surface of both the 3/16" and 1/4" tubingpassed 1,100 hours before forming red rust build up larger than 1 mm indiameter, using Standard Method of Salt Spray (Fog) Testing ASTM B117-73.

EXAMPLE IX

3/16" and 1/4" brazed steel tubing are prepared according to Example I,where two layers of Nylon 12 having a total thickness between about0.005 inch to 0.010 inch are applied to each of the tubes. Each of the3/16" and 1/4" tube ends are placed through a 0.213" diameter entrybushing and a 0.275" diameter entry bushing, respectively, into aWD-1LTC-100 (100 Watt) Laser Wire Stripper modified with the defocusinglens discussed hereinabove. The laser beam is activated to impinge theouter circumference of the end of each of the non-rotating tubes, and,in 3.5 seconds, a length of 6 mm of both layers of Nylon 12 is removedfrom the outer circumference of the ends, leaving a tapered transitionportion having a length of 1.27 mm. Under electron beam microscopeanalysis, it is determined that the GALFAN/phosphate coating isundamaged. The tubes have a satisfactory amount of Nylon 12 removed toprepare them for subsequent SAE or ISO endforming.

EXAMPLE X

3/16" and 1/4" tubing are prepared as in Example IX. An ultra thin,shiny polymeric residue is detected on the laser removed surface of eachtube. The laser removed surface of both the 3/16" and 1/4" tubing passes1,100 hours before forming red rust build up larger than 1 mm indiameter, using Standard Method of Salt Spray (Fog) Testing ASTM B117-73.

While the invention has been described in connection with what ispresently considered to be the most practical and preferred embodiments,it is to be understood that the invention is not to be limited to thedisclosed embodiments but, on the contrary, is intended to cover variousmodifications and equivalent arrangements included within the spirit andscope of the appended claims, which scope is to be accorded the broadestinterpretation so as to encompass all such modifications and equivalentstructures as is permitted under the law.

What is claimed is:
 1. A method for preparing a multi-layer tube,comprising the step of:substantially removing at least a portion of apolymeric layer from an outer surface circumference of a metal tubehaving a corrosion resistant layer applied thereto, by axiallydefocusing a laser beam from a pinpoint cross-sectional shape to agenerally elliptical cross-sectional shape onto the polymeric layerportion, wherein the generally elliptical cross-sectionally shaped laserbeam vaporizes the polymeric layer portion while leaving the corrosionresistant layer intact; wherein the multi-layer tube is at least one ofa brakeline, a vacuum line, a transmission oil cooler line, a vaporreturn line, and a fuel line.
 2. A method for preparing a multi-layertube, comprising the step of:substantially removing at least a portionof a polymeric layer from an outer surface circumference of a metal tubehaving a corrosion resistant layer applied thereto, by axiallydefocusing a laser beam from a pinpoint cross-sectional shape to agenerally elliptical cross-sectional shape onto the polymeric layerportion, wherein the generally elliptical cross-sectionally shaped laserbeam vaporizes the polymeric layer portion while leaving the corrosionresistant layer intact; wherein the axial defocusing is accomplished bya beam delivery system, the system comprising:a laser beam generatoremitting the pinpoint cross-sectionally shaped laser beam; means,operatively connected to the beam generator, for defocusing the pinpointcross-sectionally shaped laser beam into the generally ellipticalcross-sectionally shaped laser beam; and means, operatively connected tothe beam generator and the defocusing means, for reflecting one of thepinpoint cross-sectionally shaped laser beam and the generallyelliptical cross-sectionally shaped laser beam to a position adjacentthe polymeric layer portion.
 3. The method as defined in claim 2 whereinthe laser beam enters the reflecting means along an axis, and whereinthe reflecting means comprises:a generally C-shaped housing whichrotates 360° about the axis, the housing having a laser beam entry and alaser beam exit; and a mirror system disposed within the housing, themirror system adapted to reflect one of the pinpoint cross-sectionallyshaped laser beam and the generally elliptical cross-sectionally shapedlaser beam from the entry to the exit.
 4. The method as defined in claim3 wherein the defocusing means comprises a defocusing lens disposedwithin the housing.
 5. The method as defined in claim 4 wherein thedefocusing lens comprises a ZnSe 2.5 inch focal length×0.750 inchcylindrical diameter lens.
 6. The method as defined in claim 4 whereinthe mirror system reflects the pinpoint cross-sectionally shaped laserbeam, the defocusing lens is mounted adjacent the laser beam exit, andthe generally elliptical cross-sectionally shaped laser beam is emittedthrough the laser beam exit.
 7. The method as defined in claim 6 whereinan end of the multi-layer tube is positioned adjacent the laser beamexit, and the multi-layer tube is centered on the axis.
 8. The method asdefined in claim 7 wherein the generally elliptical shaped cross-sectionof the laser beam has two sides, and wherein one side is more curvedthan the other side.
 9. The method as defined in claim 8 wherein theother side is generally pointed.
 10. The method as defined in claim 8wherein the polymeric layer portion has a first area adjacent the tubeend and a second area distal from the tube end, and wherein the one sidesubstantially contacts the first area, and the other side substantiallycontacts the second area.
 11. The method as defined in claim 10, furthercomprising a generally tapered transition portion of the polymericlayer, extending from an upper surface of the polymeric layer toward themetal tube outer surface circumference.
 12. The method as defined inclaim 11 wherein the length of the transition portion is less than about2 mm (0.08").
 13. The method as defined in claim 12 wherein the lengthof the transition portion is approximately 1.27 mm (0.05").
 14. A methodfor preparing a multi-layer tube, comprising the step of:substantiallyremoving at least a portion of a polymeric layer from an outer surfacecircumference of a metal tube having a corrosion resistant layer appliedthereto, by axially defocusing a laser beam from a pinpointcross-sectional shape to a generally elliptical cross-sectional shapeonto the polymeric layer portion, wherein the generally ellipticalcross-sectionally shaped laser beam vaporizes the polymeric layerportion while leaving the corrosion resistant layer intact, wherein themetal tube is substantially non-rotating during removal of the polymericlayer portion.
 15. The method as defined in claim 1, further comprisingan ultra thin, corrosion resistance-enhancing polymeric residue on adiscrete area of the metal tube outer surface circumference afterpolymeric layer portion removal therefrom.
 16. The method as defined inclaim 15 wherein the ultra thin residue has a thickness sufficient toenhance the corrosion resistance of the laser removed metal tube outersurface circumference such that the laser removed metal tube outersurface passes up to about 1,100 hours of Standard Method of Salt Spray(Fog) Testing, ASTM Designation: B 117-73, published June 1973, beforeforming red rust build up larger than about 1 mm (0.04") in diameter.17. The method as defined in claim 1 wherein the polymeric layer portionremoved has a length ranging between about 1 mm (0.04") and about 76.2mm (3").
 18. The method as defined in claim 17 wherein the polymericlayer portion removed has a length ranging between about 4 mm (0.157")and about 8 mm (0.315").
 19. The method as defined in claim 18 whereinthe polymeric layer portion removed has a length ranging between about 6mm (0.236") and about 7 mm (0.276").
 20. The method as defined in claim1 wherein the polymeric layer has a thickness ranging between about 170microns (0.0068") and about 202 microns (0.0081").
 21. The method asdefined in claim 1 wherein the metal tube is a steel tube.
 22. Themethod as defined in claim 1 wherein the polymeric layer portion removalis accomplished in a single pass.
 23. The method as defined in claim 1wherein the polymeric layer portion removal is accomplished in a timeranging between about 1 second and about 4 seconds.
 24. The method asdefined in claim 23 wherein the polymeric layer portion removal isaccomplished in approximately 3.5 seconds.
 25. A method for preparing amulti-layer tube, comprising the step of:substantially removing at leasta portion of a polymeric layer from an outer surface circumference of ametal tube having a corrosion resistant layer applied thereto, byaxially defocusing a laser beam from a pinpoint cross-sectional shape toa generally elliptical cross-sectional shape onto the polymeric layerportion, wherein the generally elliptical cross-sectionally shaped laserbeam vaporizes the polymeric layer portion while leaving the corrosionresistant layer intact; wherein the multi-layer tube is a high pressurefluid conduit having two ends, the polymeric layer portion is removedfrom each end, and wherein the method further comprises the stepof:endforming each of the conduit two ends into a double or invertedflare, wherein each of the flares is formed approximately where thepolymeric layer portion is removed.
 26. The method as defined in claim25 wherein the conduit is a brakeline.
 27. A method for preparing amulti-layer tube, comprising the step of:substantially removing at leasta portion of a polymeric layer from an outer surface circumference of ametal tube having a corrosion resistant layer applied thereto, byaxially defocusing a laser beam from a pinpoint cross-sectional shape toa generally elliptical cross-sectional shape onto the polymeric layerportion, wherein the generally elliptical cross-sectionally shaped laserbeam vaporizes the polymeric layer portion while leaving the corrosionresistant layer intact; wherein the multi-layer tube is a high pressurefluid conduit having two ends, the polymeric layer portion is removedfrom each end, and wherein the method further comprises the stepof:endforming each of the conduit two ends into an annularly protrudingflare, wherein each of the flares is formed approximately where thepolymeric layer portion is removed.
 28. The method as defined in claim27 wherein the conduit is a brakeline.
 29. A method for preparing amulti-layer tube, comprising the step of:substantially removing at leasta portion of a polymeric layer from an outer surface circumference of ametal tube having a corrosion resistant layer applied thereto, byaxially defocusing a laser beam from a pinpoint cross-sectional shape toa generally elliptical cross-sectional shape onto the polymeric layerportion, wherein the generally elliptical cross-sectionally shaped laserbeam vaporizes the polymeric layer portion while leaving the corrosionresistant layer intact; wherein the corrosion resistant layer comprisesa zinc layer bonded to the metal tube outer surface, wherein the zinclayer is selected from the group consisting of zinc plating, zinc nickelalloys, zinc cobalt alloys, zinc aluminum alloys, and mixtures thereof;and wherein the multi-layer tube further comprises a surface treatmentlayer bonded to the zinc layer, wherein the surface treatment layer isselected from the group consisting of a zinc aluminum rare earth alloy,phosphate, chromate, and mixtures thereof.
 30. The method as defined inclaim 29 wherein the zinc aluminum rare earth alloy of the surfacetreatment layer consists essentially of:between about 85% and about 97%Zn; between about 4% and about 15% Al; and at least about 5 ppm of arare earth-containing alloy.
 31. The method as defined in claim 30wherein the multi-layer tube further comprises:a first polymeric layerbonded to the surface treatment layer, wherein the first polymeric layeris selected from the group consisting of thermoplastic elastomers,ionomers, nylons, fluoropolymers, and mixtures thereof; and a secondpolymeric layer bonded to the first polymeric layer, wherein the secondpolymeric layer is selected from the group consisting of nylons,thermoplastic elastomers, fluoropolymers, and mixtures thereof.
 32. Themethod as defined in claim 31, further comprising a third polymericlayer interposed between, and bonded to the first and second polymericlayers, wherein the third polymeric layer is selected from the groupconsisting of ionomers, nylons, ethylene vinyl alcohol, polyolefins, andmixtures thereof.
 33. The method as defined in claim 32 wherein the zinclayer has a thickness ranging between about 10 to 25 microns, thesurface treatment layer has a weight ranging between about 37.3 g/m² andabout 97.7 g/m², and wherein the first and second polymeric layers,combined, have a thickness ranging between about 75 microns and about300 microns.
 34. The method as defined in claim 32 wherein the first,second and third polymeric layers, combined, have a thickness rangingbetween about 75 microns and about 300 microns.
 35. A method forpreparing a multi-layer tube, comprising the step of:removing at least aportion of a first polymeric layer and a second polymeric layer from anouter surface circumference of a metal tube, by contacting the portionof the first and second polymeric layers with a laser beam, wherein thelaser beam vaporizes the portion of the first and second polymericlayers without harm to the outer surface of the metal tube, and whereinthe metal tube is substantially non-rotating during removal of theportion of the first and second polymeric layers.
 36. The method asdefined in claim 35 wherein the metal tube is a steel tube.
 37. A methodfor preparing a multi-layer tube, comprising the step of:removing atleast a portion of a first polymeric layer and a second polymeric layerfrom an outer surface circumference of a metal tube, by contacting theportion of the first and second polymeric layers with a laser beam,wherein the laser beam vaporizes the portion of the first and secondpolymeric layers without harm to the outer surface of the metal tube;wherein the first polymeric layer is bonded to the metal tube outersurface, the first polymeric layer being selected from the groupconsisting of thermoplastic elastomers, ionomers, nylons,fluoropolymers, and mixtures thereof; and wherein the second polymericlayer is bonded to the first polymeric layer, the second polymeric layerbeing selected from the group consisting of nylons, thermoplasticelastomers, fluoropolymers, and mixtures thereof.
 38. The method asdefined in claim 37, further comprising a third polymeric layerinterposed between, and bonded to the first and second polymeric layers,wherein the third polymeric layer is selected from the group consistingof ionomers, nylons, ethylene vinyl alcohol, polyolefins, and mixturesthereof.
 39. The method as defined in claim 38 wherein each of thefirst, second and third polymeric layers has a thickness ranging betweenabout 10 microns and about 250 microns.
 40. The method as defined inclaim 39 wherein the first polymeric layer consists essentially of anionomer and a nylon.
 41. The method as defined in claim 40 wherein theionomer is ethylene methacrylic acid copolymer--partial metal salt, andwherein the nylon is Nylon
 12. 42. The method as defined in claim 41wherein the ethylene methacrylic acid copolymer--partial metal saltcomprises between about 10% and about 70% of the first polymeric layer,and wherein the Nylon 12 comprises between about 90% and about 30% ofthe first polymeric layer.
 43. The method as defined in claim 39 whereinthe second polymeric layer consists essentially of Nylon
 12. 44. Amethod for preparing a multi-layer, high pressure fluid conduit, themethod comprising the steps of:forming a brazed steel tube having anouter surface and an end; bonding a corrosion resistant layer to thesteel tube outer surface; bonding a surface treatment layer to thecorrosion resistant layer; extruding a first polymeric layer onto thesteel tube, such that it bonds to the surface treatment layer; extrudinga second polymeric layer onto the steel tube, such that it bonds to thefirst polymeric layer; and vaporizing and removing at least a portion ofthe first and second polymeric layers from an area adjacent the end byrotating an axially defocused, generally elliptical cross-sectionallyshaped laser beam 360° about the area, while leaving the corrosionresistant layer intact.
 45. The method as defined in claim 44 whereinthe conduit is a brakeline, and wherein the method further comprises thestep of endforming each of the metal tube two ends into a double orinverted flare, wherein each of the flares is formed approximately wherethe portion of the first and second polymeric layers is removed.
 46. Themethod as defined in claim 44 wherein the conduit is a brakeline, andwherein the method further comprises the step of endforming each of themetal tube two ends into an annularly protruding flare, wherein each ofthe flares is formed approximately where the portion of the first andsecond polymeric layers is removed.
 47. A method for preparing amulti-layer tube, comprising the step of:removing at least a portion ofa polymeric layer from an outer surface circumference of a metal tube,by contacting the portion of the polymeric layer with a laser beam,wherein the laser beam simultaneously vaporizes substantially the entireouter surface circumference polymeric layer portion without harm to theouter surface of the metal tube, wherein the metal tube is substantiallynon-rotating during removal of the polymeric layer portion.
 48. Themethod as defined in claim 47 wherein the metal tube is a steel tube.49. A method for preparing a multi-layer tube, comprising the stepof:removing at least a portion of a polymeric layer from an outersurface circumference of a metal tube, by contacting the portion of thepolymeric layer with a laser beam, wherein the laser beam simultaneouslyvaporizes substantially the entire outer surface circumference polymericlayer portion without harm to the outer surface of the metal tube;wherein the polymeric layer comprises a first polymeric layer and asecond polymeric layer, and wherein the first polymeric layer is bondedto the metal tube outer surface, the first polymeric layer beingselected from the group consisting of thermoplastic elastomers,ionomers, nylons, fluoropolymers, and mixtures thereof; and wherein thesecond polymeric layer is bonded to the first polymeric layer, thesecond polymeric layer being selected from the group consisting ofnylons, thermoplastic elastomers, fluoropolymers, and mixtures thereof.50. The method as defined in claim 49 wherein the metal tube issubstantially non-rotating during removal of the polymeric layerportion.
 51. The method as defined in claim 49 wherein the metal tube issubstantially rotating during removal of the polymeric layer portion.52. The method as defined in claim 49 wherein the first polymeric layerconsists essentially of an ionomer and a nylon.
 53. The method asdefined in claim 52 wherein the ionomer is ethylene methacrylic acidcopolymer--partial metal salt, and wherein the nylon is Nylon
 12. 54.The method as defined in claim 53 wherein the ethylene methacrylic acidcopolymer--partial metal salt comprises between about 10% and about 70%of the first polymeric layer, and wherein the Nylon 12 comprises betweenabout 90% and about 30% of the first polymeric layer.
 55. The method asdefined in claim 49 wherein the second polymeric layer consistsessentially of Nylon
 12. 56. The method as defined in claim 49, furthercomprising a third polymeric layer interposed between, and bonded to thefirst and second polymeric layers, wherein the third polymeric layer isselected from the group consisting of ionomers, nylons, ethylene vinylalcohol, polyolefins, and mixtures thereof.
 57. The method as defined inclaim 56 wherein each of the first, second and third polymeric layershas a thickness ranging between about 10 microns and about 250 microns.